This project investigates motor and cognitive aspects of infants' manual control. The acquisition of reaching and grasping skills is a principal achievement during infancy, yet its development is still not well understood. The focus of this project is on the effects of vision in reaching because of the central role vision plays in specifying spatial location of object and hands. During infancy vision also confirms the existence of both objects and spatial surround in the context of Piagetian theory. This project has two broad objectives: to delineate and describe how infants use visual and proprioceptive information to control reaching for objects, and (2) to determine the interplay between motor skills and .cognitive abilities in infants' reaching for unseen objects. Infants between 2 and 13 months of age will tested while reaching for objects in the light and for luminous and sounding (nonluminous) objects in the dark. Objects will differ in size, orientation, and location. The approach and grasp of objects under various conditions should reveal whether infants prepare their hand appropriately to grasp an object when they can see both object and hand, only the object, or neither. Overt behavior will be videotaped and analyzed for interactions with the object. In addition a detailed analysis of hand movement during the reach by means of a motion analysis system will yield velocity, acceleration, and distance in 3-dimensional space for hand and object. Cognitive abilities can be inferred from certain aspects of motor activity, such as hand shaping and the approach .trajectory for an unseen object in the dark. The manner in which infants use proprioceptive and visual information to control reaching has implications both for blind children who are forced to rely on non-visual information and for patients who have lost proprioceptive control through accident or disease. Understanding how visual-motor control is achieved early in development should aid rehabilitation plans for subjects who must relearn neuromuscular control under disturbed circumstances.